Characterization of defect in multi layers by pulsed eddy current

In contrast to conventional eddy current methods, pulsed eddy current (PEC) excites the probe's driving coil with a repetitive broadband pulse, such as a square wave. The resulting transient current through the coil induces transient eddy currents in the test piece, associated with highly attenuated magnetic pulses propagating through the material. At each probe location, a series of voltage-time data pairs are produced as the induced field decays, since a broad frequency spectrum is produced in one pulse, the reflected signal contains depth information of the material. Physically, the pulse is broadened and delayed as it travels deeper into the highly depressive material. Therefore, flaws or other anomalies close to the surface will affect the eddy current response earlier in time than deep flaws. The modes of presentation of PEC data in the form of A-, and C-scans. Interpretation, therefore, may be considered more intuitive than conventional eddy current data. PEC methods are very flexible: The excitation pulse, signal gain and sensor configurations can be modified to suit particular applications.